hw8 - CSCI 415 Data Communication Networks Homework 8...

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CSCI 415 Data Communication Networks Homework 8 05/14/08 Saad Mneimneh Visiting Professor Hunter College of CUNY Problem 1: MIMD (optional) This problem is inspired by a question asked in class. Consider an conges- tion control algorithm that always uses slow start to increase the window size. Therefore: on ACK : cwnd = cwnd + 1 on timeout : cwnd = cwnd/ 2 (a) Under what circumstances is the fast retransmit mechanism not effective? (b) Suppose that the timeout is equal to α × RTT (in practice α could be as large as 20). Show by constructing an example that the effective throughput of this congestion control algorithm could be as low as (assuming a unit of bandwidth) 2 α + 1 Problem 2: Random Early Detection Consider a RED gateway with MaxP = 0 . 02, and with an average queue length halfway between the two thresholds. Recall that p is computed as Q avg - Q min Q max - Q min MaxP and p count = p 1 - count × p , where count is the number of pack- ets that are queued since the last drop while
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This note was uploaded on 03/27/2010 for the course CSCI 415 taught by Professor Saadmneimneh during the Spring '08 term at CUNY Hunter.

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hw8 - CSCI 415 Data Communication Networks Homework 8...

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